Received Signal Strength Indication (RSSI) is a measurement of the power present in a received radio signal. The RSSI measurements are used by a wireless communications device to determine the signal strengths of radio signals emanating from base stations in the vicinity of the device. The RSSI measurements enable the device to ascertain which base station is currently providing the optimal wireless link and when to perform a handover from one base station to another.
In a typical time division multiple access (TDMA) radio-access technology (RAT) implementation, such as GSM/GPRS/EDGE, at least one RSSI measurement is made per frame for voice calls or data transfer. Thus, for a GSM-based implementation, since each GSM frame has only 8 timeslots, an RSSI measurement must be scheduled within one or more of the timeslots. Where only a single downlink slot and a single uplink slot are used, there is generally no problem scheduling at least one RSSI measurement per GSM frame.
However, GPRS/EGPRS wireless devices and mobile phones may utilize multislot classes. This technology enables more than one downlink timeslot or more than one uplink timeslot per frame. A multislot class can have a value between 1 and 45. For example, a class 10 multislot device, which is currently quite prevalent, uses a maximum of 4 timeslots in the downlink direction and 2 timeslots in the uplink direction. However, the total number of timeslots per frame may not, for class 10, exceed 5. Thus, the network configures either 4 Rx+1 Tx or 3 Rx+2 Tx (meaning 4 downlink slots plus 1 uplink slot, or 3 downlink slots plus 2 uplink slots). Multislot classes with a class rating of 31 or higher are deemed to be high (or “higher”) multislot classes. These higher multislot classes are to utilize 6 or 7 timeslots per frame for either uplink or downlink. For example, a multislot class 32 would employ 5 downlink slots and 3 uplink slots with a maximum of 6 timeslots.
In these higher multislot classes, however, there is generally insufficient space to perform an RSSI measurement because of the substantial time required to stabilize the phase-locked loop of the receiver. One inadequate solution would be to implement a highly advanced and expensive PLL design in the device; however, this is not cost-effective for consumer wireless devices. Another solution would be to employ more than one receiver, but the use of an extra transceiver chip is not only expensive but also adds unwanted bulk to the device. For Evolved EDGE, which will require a second receiver, operating both receivers consumes more power than would be desirable. There is therefore a need for a solution to one or more of the foregoing problems.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.